Duke:

You can tell we did mostly Ford and imports in our home garage....

Replacing guides if you have the press and pilots is easy. No way to do it safely without, although I have seen and heard of guides being replaced in situ when one came adrift in the head. Scary, as you can bugger the head if you screw up, and it's rather likely the valve won't seat properly. Better than with the guide floating around, though!

MB guides almost never need to be reamed -- factory clearance spec is 0.00 to 0.01mm -- essentially, if you can get an oiled valve stem in it by hand, it's fine. Any more clearance and they suck oil down the valve guides.

Haven't checked on the aluminum heads, but on the deisels with cast iron heads, the intake guide is steel and the exhaust guide is bronze.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!